ch 2 is matter around us pure

Question 1

what does a scientist mean when a substance is pure

Answer 1

When a scientist says that something is pure, it means that all the constituent particles of that substance are the same in their chemical

Question 2

what is a mixture?

Answer 2

When two or more substances (elements, compounds or both) are physically mixed together in any proportion, such that they do not undergo any chemical change, but retain their individual characteristics, the resulting product is called a mixture.

Question 3

what is a solution ?

Answer 3

solution is a homogeneous mixture of two or more substances.

Question 4

define alloy

Answer 4

alloy are mixture of two or more metals or a metal and a non-metal is known as alloy. They can’t be separated to their original by physical methods.

for e.g. brass is made up of 30% zinc and 70% copper

Question 5

what are the two parts of solution

Answer 5

solute and solvent

Question 6

define solvent

Answer 6

The component of the solution
that dissolves the other component in it
(usually the component present in larger
amount) is called the solvent.

Question 7

define solute

Answer 7

The component
of the solution that is dissolved in the solvent
(usually present in lesser quantity) is called
the solute.

Question 8

what are the properties of a solution?

Answer 8

• A solution is a homogeneous mixture.
• The particles of a solution are smaller
than 1 nm (10^-9 metre) in diameter. So,
they cannot be seen by naked eyes.
• Because of very small particle size, they
do not scatter a beam of light passing
through the solution. So, the path of
light is not visible in a solution.
• The solute particles cannot be
separated from the mixture by the
process of filtration. The solute particles
do not settle down when left undisturbed,
that is, a solution is stable

Question 9

what is a saturated solution?

Answer 9

a solution that has dissolved as much solute as it is
capable of dissolving, is said to be a saturated
solution. In other words, when no more solute
can be dissolved in a solution at a given
temperature, it is called a saturated solution

Question 10

what is unsaturated solution?

Answer 10

If the amount of solute contained in a
solution is less than the saturation level, it is
called an unsaturated solution

Question 11

what is the concentration of a solution?

Answer 11

The concentration of a solution is the amount
(mass or volume) of solute present in a given
amount (mass or volume) of solution

Question 12

what’s the formula for finding the concentration of a solution by mass?

Answer 12

Mass by mass percentage of a solution
Mass of solute
———————– x 100
Mass of solution

Question 13

what’s the formula for finding concentration of a solution by Mass and volume?

Answer 13

Mass by volume percentage of a solution
Mass of solute
—————————- x100
Volume of solution

Question 14

what’s the formula for finding the concentration of a solution by volume?

Answer 14

Volume by volume percentage of a
solution
Volume of solute
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ x 100
Volume of solution

Question 15

what kind of a mixture is a suspension?

Answer 15

A suspension is a heterogeneous
mixture in which the solute particles do not
dissolve but remain suspended throughout
the bulk of the medium. Particles of a
suspension are visible to the naked eye.

Question 16

what are the properties of suspension ?

Answer 16

• Suspension is a heterogeneous
mixture.
• The particles of a suspension can be seen
by the naked eye.
• The particles of a suspension scatter a
beam of light passing through it and
make its path visible.
• The solute particles settle down when a
suspension is left undisturbed, that is,
a suspension is unstable. They can be
separated from the mixture by the
process of filtration. When the particles
settle down, the suspension breaks and
it does not scatter light any more.

Question 17

what are the properties of a colloid ?

Answer 17

Properties of a colloid
• A colloid is a heterogeneous mixture.
• The size of particles of a colloid is too
small to be individually seen by naked
eyes.
• Colloids are big enough to scatter a
beam of light passing through it and
make its path visible.
• They do not settle down when left
undisturbed, that is, a colloid is quite
stable.
• They cannot be separated from the
mixture by the process of filtration. But,
a special technique of separation known
as centrifugation (perform activity 2.5),
can be used to separate the colloidal
particles

Question 18

name the various ways heterogeneous mixtures can be separated?

Answer 18

Heterogeneous mixtures can be separated
into their respective constituents by simple
physical methods like handpicking, sieving,
filtration that we use in our day-to-day life.
Sometimes special techniques have to be used
for the separation of the components of a
mixture.

Question 19

explain how centrifugation works

Answer 19

The principle
is that the denser particles are forced to the
bottom and the lighter particles stay at the
top when spun rapidly.

Question 20

Give two examples of APPLICATIONS of centrifugation in real life

Answer 20

Applications
• Used in diagnostic laboratories for
blood and urine tests.
• Used in dairies and home to separate
butter from cream.
• Used in washing machines to squeeze
out water from wet clothes

Question 21

how do immiscible liquids work?

Answer 21

The principle is that immiscible liquids
separate out in layers depending on their
densities.

Question 22

what is chromatography?

Answer 22

This process of separation of components
of a mixture is known as chromatography.
Kroma in Greek means colour. This technique
was first used for separation of colours, so
this name was given. Chromatography is the
technique used for separation of those solutes
that dissolve in the same solvent.

Question 23

give 2 applications if immiscible liquids

Answer 23

Applications
• To separate mixture of oil and water.
• In the extraction of iron from its ore,
the lighter slag is removed from the
top by this method to leave the molten
iron at the bottom in the furnace.

Question 24

give 2 real life examples of chromatography

Answer 24

Applications
To separate
• colours in a dye
• pigments from natural colours
• drugs from blood.

Question 25

give reason how to separate 2 mixable liquids

Answer 25

for the separation of components of a mixture
containing two miscible liquids that boil
without decomposition and have sufficient
difference in their boiling points.

Question 26

explain crystallization with example

Answer 26

Crystallisation is a
process that separates a pure solid in the form
of its crystals from a solution. Crystallisation
technique is better than simple evaporation
technique as –
• some solids decompose or some, like
sugar, may get charred on heating to
dryness.
• some impurities may remain dissolved
in the solution even after filtration. On
evaporation these contaminate the
solid.
Applications
• Purification of salt that we get from sea
water.
• Separation of crystals of alum (phitkari)
from impure samples.

Question 27

what is a pure substance?

Answer 27

A homogeneous material which contains particles of only one kind and has a definite set of properties,is called a pure substance e.g. Oxygen, iron, sulphur etc.

Question 28

What are the characteristics of a pure substance (mixture)?

Answer 28

Characteristics of pure substances

(1) A pure substance is homogeneous in nature.
(2) A pure substance has a definite set of properties.
(3) The composition of a pure substance cannot be altered by any physical means.
(4) A pure substance has a definite melting point, density, boiling point etc. For example, water is a pure substance because it has uniform composition throughout. It consists of only one kind of particles called water molecules, which cannot be separated into its constitue (H & O) by any simple physical process.

Question 29

what are the characteristics of mixtures ?

Answer 29

Characteristics of mixtures

(1) A mixture may be homogeneous or heterogeneous.
(2) The constituents of a mixture can be separated by physical means like filtration, evaporation.sublimation and magnetic separation.
(3) In the preparation of a mixture energy is neither evolved nor absorbed.
(4) A mixture has no definite melting point and boiling point.
(5) The constituents of a mixture retain their original set of properties. For example, magnet attracts iron fillings in a mixture of sand and iron fillings.

Question 30

what are the two types of pure substance ?

Answer 30

element and compound

Question 31

explain the classification of mixtures ?

Answer 31

homogenous and heterogenous